Scanned linear illumination of distant objects

ABSTRACT

Apparatus and associated methods relate to projecting a linear beam onto a distant object. One or more laser diodes are configured to emit one or more elliptical beams of light in an emission direction. If more than one laser diodes are used, they are aligned so as to have coplanar emission facets and common slow-axis and fast-axis directions, which are perpendicular to one another and to the emission direction. A first cylindrical lens is configured to receive the emitted beam(s) and to collimate the emitted beam(s) in the fast-axis direction perpendicular to a slow-axis direction. A second cylindrical lens is configured to receive the emitted beam(s) and to diverge the emitted beam(s) in the slow-axis direction such that if more than one beams are emitted, they are diverged so as to overlap one another in the slow-axis direction.

BACKGROUND

Each year, significant time and money are lost due to commercialaircraft accidents and incidents during ground operations, of whichsignificant portions occur during taxiing maneuvers. During groundoperations, aircraft share the taxiways with other aircraft, fuelvehicles, baggage carrying trains, mobile stairways and many otherobjects. Aircrafts often taxi to and/or from fixed buildings and otherfixed objects. Should an aircraft collide with any of these objects, theaircraft must be repaired and recertified as capable of operation. Thecost of repair and recertification, as well as the lost opportunitycosts associated with the aircraft being unavailable for use can be veryexpensive.

Pilots are located in a central cockpit where they are well positionedto observe objects that are directly in front of the cabin of theaircraft. Objects that are not located directly in front of the cabin,however, can be more difficult to observe. Wings are attached to thecabin behind the cockpit and extend laterally from the cabin in bothdirections. Some commercial and some military aircraft have largewingspans, and so the wings on these aircraft laterally extend a greatdistance from the cabin and are thus positioned behind and out of thefield of view of the cockpit. Some commercial and some military planeshave engines that hang below the wings of the aircraft. Pilots,positioned in the cabin, can have difficulty knowing the risk ofcollisions between objects external to the aircraft and the wingtipsand/or engines.

There are various types of on-ground operations that an aircraft mustperform at an airport, each of which present different collision risksto the aircraft. The taxi-in and taxi-out phases require that theaircraft move between the runway and the terminal gates, for example.During taxi-in, the aircraft must first transition from the runway to ataxiway and then to the gateway. Sometimes, the taxiway can include anelaborate network of roads requiring the aircraft to travel overstraight stretches as well as turns and transitions to/from the taxiway.Some high-speed taxi operation occurs on one-way taxiways dedicated toaircraft only. During such high-speed taxi operation, relatively distantobjects located in the forward direction of the aircraft might presentthe greatest risk of collision to the aircraft. During low-speed taxiingand gateway approach, nearby objects in the vicinity of the wings andengine nacelles might present the greatest risk of collision to theaircraft.

SUMMARY

Apparatus and associated methods relate to a system for projecting alinear beam of light on a distant object. The system includes a laserdiode bar having a plurality of laser diodes distributed along a commontransverse axis. Each of the plurality of laser diodes is configured toemit a beam of light in an emission direction orthogonal to thetransverse axis. The emitted beam diverges at a first divergence anglein a fast-axis direction orthogonal to both the transverse axis and theemission direction, and diverges in a slow-axis direction at a seconddivergence angle less than the first divergence angle. The slow-axisdirection is parallel to the transverse axis. The system includes afirst cylindrical lens configured to collimate and/or focus, in afast-axis direction, the beam of light emitted by each of the laserdiodes. The system includes a second cylindrical lens configured todiverge, in a slow-axis direction, the beam of light emitted by each ofthe plurality of laser diodes such that the beams of light emitted bythe plurality of laser diodes overlap one another in the slow-axisdirection.

Some embodiments relate to a method for projecting a linear beam oflight on a distant object. The method includes emitting, by each of aplurality of laser diodes distributed along a common transverse axis, abeam of light in an emission direction. Then, each of the plurality ofbeams of light are collimated and/or focused, in a fast-axis directionorthogonal to both the transverse axis and the emission direction, Eachof the plurality of beams of light are also diverged, in a slow-axisdirection parallel to the transverse axis, so as to span a seconddivergence angle less than the first divergence angle. Each of thediverged beams of light overlap one another in the slow-axis direction.

Some embodiments relate to a system for projecting a linear beam oflight on a distant object. The system includes at least one laser diode,each configured to emit light in an emission direction, the emittedlight diverging in a first transverse direction at a first divergenceangle and diverging in a second transverse direction at a seconddivergence angle greater than the first divergence angle. The first andsecond transverse directions are perpendicular both to the emissiondirection and to each other. The system includes optics in operablecommunication with the at least one laser diode and configured todirect, in a projection direction, the light emitted by the at least onelaser diode into a beam having a FWHM beam dimension in the firsttransverse direction is greater than 100 times a FWHM beam dimension inthe second transverse direction as measured at a predetermined distancefrom the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of an aircraft collision alerting systemused by an aircraft on a taxiway.

FIG. 1B depicts an image captured by a camera of the collision alertingsystem mounted to the aircraft depicted in FIG. 1A.

FIG. 2 is a perspective view of an embodiment of a linear projectorconfigured to focus a linear beam at a predetermined distance.

FIG. 3 is a plan view of the linear projector depicted in FIG. 2.

FIG. 4 is a side-elevation view of the linear projector depicted inFIGS. 2 and 3.

FIG. 5 is a schematic diagram of a single laser diode and a projectedbeam annotated with various beam characteristics.

FIG. 6 is a perspective view of an embodiment of a bar of laser diodes,which can provide the optical energy for a linear projector configuredto focus a linear beam at a predetermined distance.

FIGS. 7A-7C depict linear projectors having various scanning mechanisms.

DETAILED DESCRIPTION

Apparatus and associated methods relate to projecting a linear beam oflight onto a distant object. One or more laser diodes are configured toemit one or more elliptical beams of light in an emission direction. Ifmore than one laser diodes are used, they are aligned so as to havecoplanar emission facets and common slow-axis and fast-axis directions,which are perpendicular to one another and to the emission direction. Afirst cylindrical lens is configured to receive the emitted beam(s) andto collimate each of the emitted beam(s) in the fast-axis directionperpendicular to a slow-axis direction. A second cylindrical lens isconfigured to receive the emitted beam(s) and to diverge the emittedbeam(s) in the slow-axis direction such that if more than one beams areemitted, they are diverged so as to overlap one another in the slow-axisdirection.

A linear beam of light is one that has a large ratio of beam dimensionsin orthogonal directions transverse to the direction of propagation. Forexample, if a light projector projects a light beam in a directionparallel with a level ground surface and the light beam has a largeazimuthal dimension and a small elevational dimension, such a light beamilluminates a rectangular area of a screen normal to the projectiondirection. The illuminated rectangular area can be called a horizontalline of illumination if the ratio between the azimuthal dimension andthe elevational dimension is much greater than the elevationaldimension. For example, if the ratio of the azimuthal dimension to theelevational dimension is greater than 50:1, 100:1, 200:1 or more, thanthe illuminated are is substantially linear. Similarly, if the lightprojector projects a light beam in a direction parallel with a levelground surface and the light beam has a small azimuthal dimension and alarge elevational dimension, such a light beam again illuminates arectangular area of a screen normal to the projection direction. But inthis scenario, the illuminated rectangular area can be called a verticalline of illumination if the ratio between the elevational dimension andthe azimuthal dimension is much greater than the elevational dimension.

Such linear beams of illumination can be used in the determination ofdistance to the object upon which the linear beams have been projected.For example, if the beam is projected from a first location of anaircraft, and a camera that is mounted at a different location on theaircraft captures images of the illumination pattern, these capturedimages can contain distance and/or range information regarding thedistant objects reflecting the linear beams. The linear beam, forexample, may appear broken in the captured images at image locationscorresponding to illumination discontinuities—edges of foregroundobjects. Furthermore, if the projected emitted linear beam is configuredso as not to be coplanar with the camera, then triangulation can be usedto determine the distances of the objects reflecting the projectedlinear beam. The locations and/or ranges can be calculated based on alocation of a projector, a location of a camera or imager, and the pixelcoordinates upon which the reflected linear beam is focused.

The linear beam can be a pulse of light projected in a linear pattern,such as, for example, a pulse having a fixed elevation angle ofprojection but having an azimuthal angle of projection between +/−25degrees or more from the nominal direction. In some embodiments, thelinear beam can be a collimated beam rastered or scanned in a directionperpendicular to the plane containing the linear beam. The linear beamis projected within a controlled field of view. This means that outsideof the controlled field of view, substantially no light energy isprojected. Herein the term linear beam indicates that light is projectedwithin the field of view in such a manner that the projected light isnot uniformly projected throughout the solid-angle of projection. Forexample, light will be primarily projected along certain azimuthaland/or elevational angles comprising a subset of the azimuthal andelevational angles within the solid-angle of light projection. Othersubsets of the solid-angle of light projection can be used for linearbeam projection.

In some embodiments, the linear beam can have a wavelength correspondingto infrared light and/or to an atmospheric absorption band. Usinginfrared light, because it is outside the visible spectrum, can minimizea distraction to a pilot who is taxiing the aircraft. Using infraredlight that has a wavelength within an atmospheric absorption band canpermit low-power projector illumination, as the illuminating power neednot compete with the sun's illumination in such an absorption band.Knowing a first location on an aircraft from which the light isprojected, a second location on an aircraft from which the reflection isimaged, and a pixel coordinate within the image corresponding to anobject from which the light is reflected permits a calculation of thelocation and/or range of that reflecting object.

FIG. 1A is a schematic view of an exemplary aircraft collision alertingsystem used by an aircraft on a taxiway. In FIG. 1A, first aircraft 10is taxiing along one-way taxiway 12. First aircraft 10 is approachingtaxiway crossing 14. Second aircraft 16 is near the taxiway crossing 14on taxiway 18. First aircraft 10 is equipped with aircraft collisionalerting system 20. Aircraft collision alerting system 20 includeslinear projector 22, camera 24, and a controller 26. In the depictedembodiment, linear projector 22 is mounted on vertical stabilizer 28 oftail 30. Linear projector 22 is configured to project linear beam 32onto a scene external to first aircraft 10, thereby illuminating objectsexternal to first aircraft 10. Linear projector 22 can be mounted atother locations on first aircraft 10 in other embodiments. Controller 26controls and/or scans the direction of projection, such that linearprojector 22 projects linear beam 32 within a controlled direction ofprojection. In the depicted embodiment, the direction of projectionspans various elevation angles of projection 34A.

The directions of projection can be orthogonal to the angular directionof the linear beam 32. For example, if linear beam 32 is in a plane thatis roughly parallel to a ground surface (e.g., projecting horizontallines on distant objects), then controller 26 can be configured to scanlinear beam 32 in an elevational manner. Conversely, if linear beam 32is in a plane that is perpendicular to a ground surface (e.g.,projecting vertical lines on distant objects), then controller 26 can beconfigured to scan linear beam 32 in an azimuthal manner. By focusinglinear beam 32 so as to form lines of illumination on distant objects,the power required for projecting linear beam 32 can be reduced.

FIG. 1B depicts an image captured by a camera of the collision alertingsystem mounted to the aircraft depicted in FIG. 1A. In FIG. 1B, capturedimage 40A has a field of view commensurate with the solid-angle ofprojection of linear beam 32. Captured image 40A depicts second aircraft16 on taxiway 18. Superimposed on taxiway 18 and second aircraft 16 arelines 32A-32D generated by linear projector 22. Because linear projector22 and camera 24 are mounted to first aircraft 10 at differentlocations, lines 32A-32D will have discontinuities 42 in captured image40A where linear beam 32 encounters objects, such as second aircraft 16.Such discontinuities 42 in captured image 40A are indicative ofdifferences in the locations and/or ranges of the objects from whichlinear beam 32 reflects.

Such aircraft collision alerting systems as described with reference toFIGS. 1A-1B have been disclosed by Rutkiewicz et al., in U.S. patentapplication Ser. No. 15/489,381, titled “Method and System for AircraftStrike Alerting, filed Apr. 17, 2017, the entire specification of whichis hereby incorporated by reference.

FIG. 2 is a perspective view of an embodiment of a linear projectorconfigured to focus a linear beam at a predetermined distance. In FIG.2, linear projector 22 includes laser diode bar 44, first convexcylindrical lens 45, first concave cylindrical lens 46, second concavecylindrical lens 48, and second convex cylindrical lens 50. Laser diodebar 44 includes a plurality of laser diodes all aligned so as to eachemit a beam in emission direction D_(E) normal to emission plane P_(E),which is coplanar with emission facets of each of the plurality of laserdiodes of laser diode bar 44. Each of the laser diodes has both afast-axis direction D_(FA) and a slow-axis direction D_(SA) that areapproximately the same as the fast-axis direction D_(FA) and slow-axisdirection D_(SA), respectively, pertaining to each of the other of theplurality laser diodes of laser diode bar 44. Various embodiments canuse more or fewer laser diodes, including one embodiment in which asingle laser diode can be used to emit an optical beam. Fast-axisdirection D_(FA), slow-axis direction D_(SA), and emission directionD_(E) are all orthogonal one to another, in the depicted embodiment.

Simultaneous pulses of optical energy are emitted by each of theplurality of laser diodes of laser diode bar 44. The simultaneouslyemitted pulses of optical energy are emitted from emission facetslocated along transverse axis 52 within emission plane P_(E). Thesimultaneously emitted pulses of optical energy form linear emissionbeam 54 having divergence in both slow-axis direction D_(SA) andfast-axis direction D_(FA). In the FIG. 2 depiction, linear emissionbeam 54 is shown as having a 60° angle of divergence as measured beforelens correction.

Linear emission beam 54 is then received by first convex cylindricallens 45. First convex cylindrical lens 45 is convex in a fast-axisdirection D_(FA) and planar in a slow-axis direction D_(SA). Such a lenscan be called a plano-convex cylindrical lens. Because the convexity offirst convex cylindrical lens 45 is aligned with fast-axis directionD_(FA), first convex cylindrical lens 45 is configured to refract linearemission beam 54 so as to change the divergence of linear emission beam54 in the fast-axis direction. For plano-convex cylindrical lenses, thebeam divergence is decreased by refraction. Thus, first convexcylindrical lens 45 decreases the divergence of received linear emissionbeam 54 in the fast-axis direction. In some embodiments, first convexcylindrical lens 45 is mounted directly onto laser diode bar 44. Someembodiments do not have first convex cylindrical lens 45.

First concave cylindrical lens 46 is configured to receive linearemission beam 54 after it is refracted by first convex cylindrical lens45. First concave cylindrical lens 46 is concave in fast-axis directionD_(FA) and planar in slow-axis direction D_(SA). Such a lens can becalled a plano-concave cylindrical lens. Because the concavity of firstconcave cylindrical lens 46 is aligned with fast-axis direction D_(FA),first concave cylindrical lens 46 is configured to refract linearemission beam 54 so as to change the divergence of linear emission beam54 in the fast-axis direction. For plano-concave cylindrical lenses, thebeam divergence is increased by refraction. Thus, first concavecylindrical lens 46 increases the divergence of received linear emissionbeam 54 in the fast-axis direction.

Second concave cylindrical lens 48 is configured to receive linearemission beam 54 after it is refracted by first concave cylindrical lens46. The depicted location of second concave cylindrical lens 48 followsfirst concave cylindrical lens 46, but in other embodiments secondconcave cylindrical lens can precede first concave cylindrical lens 46.Second concave cylindrical lens 48 is concave in the slow-axis directionD_(SA) and planar in the fast-axis direction D_(FA). Because theconcavity of second concave cylindrical lens 48 is aligned withslow-axis direction D_(SA), second concave cylindrical lens 48 isconfigured to refract linear emission beam 54 so as to change thedivergence in the slow-axis direction. In the depicted embodiment,second concave cylindrical lens 48 increases the divergence of linearemission beam 54 in the slow-axis direction. By orienting the concavityof second concave cylindrical lens 48 in the slow-axis direction, whichis the direction in which the plurality of laser diodes of laser diodebar 44 are aligned, the pulses of optical energy emitted by theindividual laser diodes of laser diode bar 44 will overlap the opticalenergy emitted by neighboring laser diodes of laser diode bar 44. Suchoverlap can result in a 100% fill factor in the projected linear beam oflight. In some embodiments, the divergence will not result in 100% fillfactor yielding a dashed linear beam of light or a linear beam havingperiodic intensity variation.

Second convex cylindrical lens 50 is configured to receive linearemission beam 54 after it is refracted by second concave cylindricallens 48. Second convex cylindrical lens 50 is convex in the fast-axisdirection D_(FA) and planar in the slow-axis direction D_(SA). Such alens can be called a plano-convex cylindrical lens. Because theconvexity of second convex cylindrical lens 50 is aligned with fast-axisdirection D_(FA), second convex cylindrical lens 50 is configured torefract linear emission beam 54 so as to change the divergence in thefast-axis direction. For plano-convex cylindrical lenses, the beamdivergence is decreased by refraction. Thus, second convex cylindricallens 50 decreases the divergence of received linear emission beam 54 inthe fast-axis direction. Although the FIG. 2 embodiment depictsplano-convex and plano-concave cylindrical lenses, various embodimentscan use other types of convex and concave cylindrical lenses.

In some embodiments, the combination of first convex cylindrical lens45, first concave cylindrical lens 46 and second convex cylindrical lens50 are configured to collimate and/or focus linear emission beam 54 inthe fast-axis direction. In some embodiments more or fewer cylindricallenses can be configured to collimate and/or focus linear emission beam54 in the fast-axis direction. In other embodiments, first convexcylindrical lens 45, first concave cylindrical lens 46 and second convexcylindrical lens 50 are configured to focus linear emission beam 54 inthe fast-axis direction so that at a predetermined distance from linearprojector 22, linear emission beam 54 has small full-widthhalf-magnitude (FWHM) width in the fast-axis direction and large FWHMlength in the slow-axis direction, thereby earning its name of “linearemission beam.” In some embodiments, such a narrow beam in the fast-axisdirection can have a FWHM width of less than 5 centimeters, 3centimeters, or 2 centimeter in the fast-axis width. At thepredetermined distance at which linear emission beam 54 is focused,linear emission beam 54 can have a large slow-axis length. For practicalpurposes the length of the beam can be considered to be very long in theslow-axis direction, having a length to width ratio exceeding 100:1,1000:1, or 10,000:1 at a distance from emission where the beam isfocused, so as not to impose a slow-axis barrier to passage of thelinear emission beam 54.

For example, in one embodiment, linear projector 22 can be configured tofocus linear emission beam 54 in the fast-axis direction D_(FA) at apredetermined distance of 150 meters while diverging linear emissionbeam 54 at 50° in the slow-axis direction D_(SA). At the predetermineddistance, the FWHM of linear emission beam 54 can be less than 1.5centimeters in the fast-axis direction D_(FA) and can be about 140meters in the slow-axis direction D_(SA). The predetermined distance atwhich a ratio of the length to width of the beam can vary in accordancewith beam illumination specifications. For example, the beam may befocused and diverged in such a manner as to cause a FWHM length to widthratio to exceed 50:1, 100:1, 500:1 or 1000:1 at a distance of 50, 80,100, 120, 200, or 300 meters from linear projector 22, for example.

Because detection of linear emission beam 54 can be used to determinerange and/or location information of objects from which the beamreflects, linear emission beam 54 should be detectable by a detector. Toensure that linear emission beam 54 is detectable, linear emission beam54 should have intensity greater than the solar irradiance level presentduring daylight conditions. The solar irradiance can be as high as100,000 lux or 1 kilowatt per square meter on bright sunny days.Focusing linear emission beam 54 in such a linear fashion as describedabove can provide local intensities of linear emission beam 54 that arein excess of the solar irradiance, at least for a portion of the solarspectrum that includes the emission spectrum of linear emission beam 54.Filtering the detection spectrum to include only the emission spectrumand a guard band on either side of the emission spectrum furtherimproves detectability of linear emission beam 54.

In some embodiments, linear emission beam 54 is in the infrared band ofthe optical spectrum. Such an emission spectrum can be used toilluminate distant objects while remaining undetectable to humans so asnot to distract pilots and ground crew. In some embodiments, linearemission beam 54 can have a spectral bandwidth as small as 2.5 nm.

FIG. 3 is a plan view of the linear projector depicted in FIG. 2. Theplan view orientation of FIG. 3 is helpful in depicting the operation oflinear projector 22 in the slow-axis direction D_(SA). In FIG. 3, linearprojector 22 includes laser diode bar 44, first convex cylindrical lens45, first concave cylindrical lens 46, second concave cylindrical lens48, and second convex cylindrical lens 50. Laser diode bar 44 includes aplurality of laser diodes all aligned so as to each emit a beam inemission direction D_(E). The plurality of laser diodes of laser diodebar 44 generates simultaneous pulses of optical energy from each of theplurality of laser diodes so as to emit laser beams from emission facetslocated along transverse axis 52. In the FIG. 3 plan view, onlydivergence in the slow-axis direction D_(SA) of linear emission beam 54can be depicted. The FWHM length L in the slow-axis direction increaseswith increasing distance from linear projector 22 due to the positivebeam divergence in the slow-axis direction.

Linear emission beam 54 is received by first convex cylindrical lens 45.First convex cylindrical lens 45 is planar in slow-axis directionD_(SA). Because of the planarity of first convex cylindrical lens 45 inthe slow-axis direction D_(SA), first convex cylindrical lens 45 doesn'tsignificantly change the divergence of linear emission beam 54 in theslow-axis direction D_(SA).

First concave cylindrical lens 46 is configured to receive linearemission beam 54 after it is refracted by first convex cylindrical lens45. First concave cylindrical lens 46 is planar in slow-axis directionD_(SA). Because of the planarity of first concave cylindrical lens 46 inthe slow-axis direction D_(SA), first concave cylindrical lens 46doesn't significantly change the divergence in of linear emission beam54 in the slow-axis direction D_(SA).

Second concave cylindrical lens 48 is configured to receive linearemission beam 54 after it is refracted by first concave cylindrical lens46. Second concave cylindrical lens 48 is concave in the slow-axisdirection D_(SA). Because the concavity of second concave cylindricallens 48 is aligned with slow-axis direction D_(SA), second concavecylindrical lens 48 is configured to refract linear emission beam 54 soas to change the divergence in the slow-axis direction. In the depictedembodiment, second concave cylindrical lens 48 increases the divergenceof linear emission beam 54 in the slow-axis direction. By orienting theconcavity of second concave cylindrical lens 48 in the slow-axisdirection, which is the direction in which the plurality of laser diodesof laser diode bar 44 are aligned, the pulses of optical energy emittedby the individual laser diodes of laser diode bar 44 will overlap theoptical energy emitted by neighboring laser diodes of laser diode bar44.

Second convex cylindrical lens 50 is configured to receive linearemission beam 54 after it is refracted by second concave cylindricallens 48. Second convex cylindrical lens 50 is planar in the slow-axisdirection D_(SA). Because of the planarity of second convex cylindricallens 50 in the slow-axis direction D_(SA), second convex cylindricallens 50 doesn't significantly change the divergence in of linearemission beam 54 in the slow-axis direction D_(SA).

FIG. 4 is a side-elevation view of the linear projector depicted inFIGS. 2 and 3. The side-elevation view orientation of FIG. 4 is helpfulin depicting the operation of linear projector 22 in the fast-axisdirection D_(FA). In FIG. 4, linear projector 22 includes laser diodebar 44, first convex cylindrical lens 45, first concave cylindrical lens46, second concave cylindrical lens 48, and second convex cylindricallens 50. Laser diode bar 44 includes a plurality of laser diodes allaligned so that, from the side-elevation perspective, the beam isemitted from a point and in emission direction D_(E). In the FIG. 4side-elevation view, only divergence in the fast-axis direction D_(FA)of linear emission beam 54 can be depicted. The FWHM width W in thefast-axis direction doesn't significantly increase with distance fromlinear projector 22 due to the non-positive beam divergence in thefast-axis direction. For collimated beams, the angle of divergence inthe fast-axis direction is approximately zero (e.g., between +/−a fewdegrees), and for focused beams, the angle of divergence in thefast-axis direction is negative. Thus, the beam narrows with increasingdistance until a projection distance approximately equal to a focalpoint of the optical system. Beyond such a focal point, the beam width Wincreases having a divergence angle therefrom approximately opposite(i.e., additive inverse) the angle of divergence as measured at thefocusing lens.

Linear emission beam 54 is received by first convex cylindrical lens 45.First convex cylindrical lens 45 is convex in a fast-axis directionD_(FA). Because the convexity of first convex cylindrical lens 45 isaligned with fast-axis direction D_(FA), first convex cylindrical lens45 is configured to refract linear emission beam 54 so as to change thedivergence of linear emission beam 54 in the fast-axis direction D_(FA).For such a convex lens configuration, the beam divergence is decreasedby refraction. Thus, first convex cylindrical lens 45 decreases thedivergence of received linear emission beam 54 in the fast-axisdirection. First convex cylindrical lens can be used in conjunction withfirst concave cylindrical lens 46 and/or second convex cylindrical lens50 to collimate and/or focus linear emission beam 54 in a fast-axisdirection, as will be described below.

First concave cylindrical lens 46 is configured to receive linearemission beam 54 after it is refracted by first convex cylindrical lens45. First concave cylindrical lens 46 is concave in fast-axis directionD_(FA). Because the concavity of first concave cylindrical lens 46 isaligned with fast-axis direction D_(FA), first concave cylindrical lens46 is configured to refract linear emission beam 54 so as to change thedivergence of linear emission beam 54 in the fast-axis direction D_(FA).For such a concave lens configuration, the beam divergence is increasedby refraction. Thus, first concave cylindrical lens 46 increases thedivergence of received linear emission beam 54 in the fast-axisdirection.

Second concave cylindrical lens 48 is configured to receive linearemission beam 54 after it is refracted by first concave cylindrical lens46. Second concave cylindrical lens 48 is planar in the fast-axisdirection D_(FA). Because the planarity of second concave cylindricallens 48 in the fast-axis direction D_(FA), second concave cylindricallens 48 doesn't significantly change the divergence in of linearemission beam 54 in the fast-axis direction D_(FA).

Second convex cylindrical lens 50 is configured to receive linearemission beam 54 after it is refracted by first concave cylindrical lens46. Second convex cylindrical lens 50 is convex in the fast-axisdirection D_(FA). Because the convexity of second convex cylindricallens 50 is aligned with fast-axis direction D_(FA), second convexcylindrical lens 50 is configured to refract linear emission beam 54 soas to change the divergence of linear emission beam 54 in the fast-axisdirection D_(FA). For such a convex lens configuration, the beamdivergence is decreased by refraction. Thus, second convex cylindricallens 50 decreases the divergence of received linear emission beam 54 inthe fast-axis direction.

In some embodiments, the combination of first concave cylindrical lens46 and second convex cylindrical lens 50 are configured to collimateand/or focus linear emission beam 54 in the fast-axis direction. Inother embodiments, first concave cylindrical lens 46 and second convexcylindrical lens 50 are configured to focus linear emission beam 54 inthe fast-axis direction so that at a predetermined distance from linearprojector 22, linear emission beam 54 has a small width in the fast-axisdirection. For example, the full-width half-magnitude (FWHM) width ofthe optical energy can be equal to or less than 5 centimeters, 3centimeters, or 2 centimeter in the fast-axis direction. At thepredetermined distance at which linear emission beam 54 is focused,linear emission beam 54 can have a large slow-axis direction.

FIG. 5 is a schematic diagram of a single laser diode and a projectedbeam annotated with various beam characteristics. In FIG. 5, laser diode44A is one of the plurality of laser diodes of laser diode bar 44depicted in FIGS. 2-4. Laser diode 44A includes semiconductor portion 56in which is formed active layer 58. Back facet 60 and emission facet 62are formed on opposite sides of active layer 58. Back facet 60 can becoated with a coating that causes near-total internal reflection ofoptical energy. Laser diode 44A is shown emitting pulse of opticalenergy 54A in emission direction DE normal to emission facet 62.

Pulse of optical energy 54A is elliptical, astigmatic, and has largedivergence. Pulse of optical energy 54A is generated in active layer 58of semiconductor portion 56 and is emitted from emission facet 62 at oneend of the active layer 58. Because active layer 58 of laser diode 44Ahas a rectangular shaped cross section—thin in the fast-axis directionD_(FA) and wide in the slow-axis direction—D_(SA) emitted pulse ofoptical energy 54A at emission facet 62 has an elliptical shape asdepicted. For example, in the depicted embodiment, pulse of opticalenergy 54A emitted at emission facet 62 is about five microns in thedirection vertical to active layer 58 (the fast-axis direction D_(FA))and hundreds of microns in the direction horizontal to active layer 58(the slow-axis direction D_(SA)).

Various embodiments use various sources of light emissions. For example,various types, geometries of laser diodes can be used to generate alinear beam of light using the lens configurations described herein.Embodiments in which the laser diodes have different dimensions, theratio of the slow-axis beam length to the fast-axis beam width can be aslarge as 50:1, 100:1 or even greater. Furthermore, non-laser-diode lightsources, such as traditional lasers or vertical-cavity surface emissionlasers can also be used to generate a linear beam of light using thelens configurations described herein.

The beam divergence, however, is greater in the fast-axis directionD_(FA) than in the slow-axis direction D_(SA). This is indicated by thefirst divergence angle θ₁ (i.e., the divergence in the fast-axisdirection) being greater than the second divergence angle θ₂ (i.e., thedivergence in the slow-axis direction). Thus, as pulse of optical energy54A propagates away from emission facet 62, the ratio of the slow-axisbeam length to the fast-axis beam width will continuously decrease. Forexample, the full width half magnitude (FWHM) divergent angle in theslow-axis direction D_(SA) can be between 6°-12°, while the FWHMdivergent angle in the fast-axis direction D_(FA) can be between15°-40°.

FIG. 6 is a perspective view of an embodiment of a bar of laser diodes,which can provide the optical energy for a linear projector configuredto focus a linear beam at a predetermined distance. In FIG. 6, laserdiode bar 44 includes laser diodes 44A-44E. Laser diodes 44A-44Egenerate beams of optical energy 54A-54E, respectively. Each of thegenerated pulses of optical energy 54A-54E is emitted in emissiondirection D_(E). As each of the emitted pulses of optical energypropagates, divergence in both the slow-axis direction D_(SA) and in thefast-axis direction D_(EA) occurs. Because divergence in the fast-axisdirection D_(EA) is greater than divergence in the slow-axis directionD_(SA), the far-field elliptical profile of the pulses are differentthan the profile of the pulses at the emission facets.

Laser diodes 44A-44E are aligned along a transverse axis that isparallel to the slow-axis direction. Although the divergence angle inthe slow-axis direction D_(SA) is small (e.g., less than 20° is notuncommon), optical pulses of energy 54A-54E will eventually combine toform a single linear emission beam 54, even without lensing. Combinedbeam 54, however, will only have a divergence in the slow-axis directionD_(SA) equal to the divergence in the slow-axis direction D_(SA) of eachof the optical pulses of energy 54A-54E. To increase the divergence inthe slow-axis direction a concave cylindrical lens can be used, as shownabove by second concave cylindrical lens 48, depicted in FIG. 2. Foreven greater divergences, cylindrical lens 48 can be a combination oftwo or more concave cylindrical lenses. Such lens configurations canprovide slow-axis divergence up to 180 degrees.

Combined beam 54 has a greater divergence in the fast-axis directionD_(EA) than in the slow-axis direction D_(SA). A plano-convex lens, suchas second convex cylindrical lens 50 depicted in FIG. 2, can be used tocollimate and/or focus combined beam 54. Once so collimated or focused,combined beam 54 can illuminate distant objects with intensities thatexceed the solar irradiance, at least over a limited bandwidth. Such aprojector can thus be used in broad daylight to determined range and orlocation information of objects external to an aircraft.

FIGS. 7A-7C depict linear projectors having various scanning mechanisms.In FIG. 7A, linear projector 22A has scanning mechanism 64A, which isconfigured to mechanically scan linear beam 32A in a fast-axisdirection. Scanning mechanism 64A includes rotational member 66, whichrotates linear projector 22A about pivot axis 68A. In some embodiments,pivot axis 68A can be parallel to the slow-axis direction D_(SA), asdepicted.

In FIG. 7B, linear projector 22B has scanning mechanism 64B, which isconfigured to optically scan linear beam 32B by reflecting linear beam32B via rotatable mirror 70. Rotatable mirror 70 is interposed in thepath of linear beam 32B. Scanning mechanism 64B is configured to rotaterotatable mirror 70 about rotation axis 68B that is parallel to theslow-axis direction D_(SA). Rotatable mirror 70 scans linear beam 32B inthe fast-axis direction (i.e., perpendicular to the linear beam 32B) asit is rotated about rotation axis 68B.

In FIG. 7C, linear projector 22C has electronic scanning capability.Linear projector 22C includes an array of laser diode bar 72 thatincludes rows of laser diodes 44A-44Z. Each of the laser diodes in aparticular row 44A-44Z is aligned along a fast-axis direction with theother laser diodes in that particular row 44A-44Z. Each of the laserdiode rows 44A-44Z can be independently energized in turn. In thedepicted embodiment laser diode row 44N is energized. Each of the laserdiode rows 44A-44Z are configured to generate a linear beam 32C of lightthat is collimated and/or focused by cylindrical lenses 45A-45N, 46 and50 in a fast-axis direction D_(FA). The linear beam emitted by each rowof laser diodes 44A-44Z is then diverged in a slow axis direction DSA,by cylindrical lens 48. For example, the laser diode rows 44A-44Z can beenergized in a sequence from top row 44A to bottom row 44Z, so as togenerate a corresponding sequence of linear beams focused at differentangles of elevation with respect to linear projector 22C.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

Apparatus and associated methods relate to a system for projecting alinear beam of light on a distant object. The system includes a laserdiode bar having a plurality of laser diodes distributed along a commontransverse axis. Each of the plurality of laser diodes is configured toemit a beam of light in an emission direction orthogonal to thetransverse axis. The emitted beam diverges at a first divergence anglein a fast-axis direction orthogonal to both the transverse axis and theemission direction, and diverges in a slow-axis direction at a seconddivergence angle less than the first divergence angle. The slow-axisdirection is parallel to the transverse axis. The system includes afirst cylindrical lens configured to collimate and/or focus, in afast-axis direction, the beam of light emitted by each of the laserdiodes. The system includes a second cylindrical lens configured todiverge, in a slow-axis direction, the beam of light emitted by each ofthe plurality of laser diodes such that the beams of light emitted bythe plurality of laser diodes overlap one another in the slow-axisdirection

The system of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing system can further include a thirdcylindrical lens configured to, in conjunction with the firstcylindrical lens, collimate and/or focus in a fast-axis direction thebeam of light emitted by each of the plurality laser diodes.

A further embodiment of any of the foregoing systems, wherein theemitted beams of light can be collimated and/or focused in the fast-axisdirection such that a full-width half-magnitude (FWHM) portion of theemitted beams of light are less than or equal to a predetermined widthin the fast-axis direction at a predetermined distance from the system.

A further embodiment of any of the foregoing systems, wherein thepredetermined distance is 150 meters from the system and thepredetermined width is 2 cm.

A further embodiment of any of the foregoing systems can further includea scanner configured to controllably pivot the linear beam of lightabout a pivot axis parallel to the slow axis.

A further embodiment of any of the foregoing systems can further includean array of laser diode bars. Each of the array of laser diode bars canhave a plurality of laser diodes distributed along a common transverseaxis. The first cylindrical lens can be configured to collimate and/orfocus the beams of light emitted by the laser diodes for each of theplurality of laser diode bars in a different fast-axis direction onefrom another.

A further embodiment of any of the foregoing systems can further includea scanner configured to selectively energized each of the plurality oflaser diode bars so as to scan the linear beam of light in a fast-axisdirection.

A further embodiment of any of the foregoing systems, wherein theemitted beam of light can have a wavelength bandwidth of less than 3 nm.

A further embodiment of any of the foregoing systems, wherein theemitted beam of light can have a nominal wavelength in the infraredband.

A further embodiment of any of the foregoing systems, wherein the firstcylindrical lens can be a concave lens with concavity in the fast-axisdirection.

A further embodiment of any of the foregoing systems, wherein the firstcylindrical lens can be a convex lens with convexity in the fast-axisdirection.

A further embodiment of any of the foregoing systems, wherein the secondcylindrical lens can be a concave lens with concavity in the slow-axisdirection.

Some embodiments relate to a Some embodiments relate to a method forprojecting a linear beam of light on a distant object. The methodincludes emitting, by each of a plurality of laser diodes distributedalong a common transverse axis, a beam of light in an emissiondirection. Then, each of the plurality of beams of light are collimatedand/or focused, in a fast-axis direction orthogonal to both thetransverse axis and the emission direction, Each of the plurality ofbeams of light are also diverged, in a slow-axis direction parallel tothe transverse axis, so as to span a second divergence angle less thanthe first divergence angle. Each of the diverged beams of light overlapone another in the slow-axis direction.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing method, wherein focusing, in afast-axis direction, each of the emitted beams of light can result in afull-width half-magnitude (FWHM) portion of the emitted beams of lightare less than or equal to a predetermined width in the fast-axisdirection at a predetermined distance from the system.

A further embodiment of any of the foregoing methods, wherein thepredetermined distance is 150 meters and the predetermined width is 2cm.

A further embodiment of any of the foregoing methods can further includecontrollably pivoting the linear beam of light about a pivot axisparallel to the slow axis.

A further embodiment of any of the foregoing methods, whereincontrollably pivoting the linear beam of light about a pivot axis caninclude mechanically pivoting a projector about the pivot axis.

A further embodiment of any of the foregoing methods, wherein theemitted beam of light can have a wavelength bandwidth of less than 3 nm.

A further embodiment of any of the foregoing methods, wherein theemitted beam of light can have a nominal wavelength in the infraredband.

Some embodiments relate to a system for projecting a linear beam oflight on a distant object. The system includes at least one laser diode,each configured to emit light in an emission direction, the emittedlight diverging in a first transverse direction at a first divergenceangle and diverging in a second transverse direction at a seconddivergence angle greater than the first divergence angle. The first andsecond transverse directions are perpendicular both to the emissiondirection and to each other. The system includes optics in operablecommunication with the at least one laser diode and configured todirect, in a projection direction, the light emitted by the at least onelaser diode into a beam having a FWHM beam dimension in the firsttransverse direction is greater than 100 times a FWHM beam dimension inthe second transverse direction as measured at a predetermined distancefrom the system.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A system for projecting a linear beam oflight on a distant object, the system comprising: a laser diode barhaving one or more laser diodes distributed along a common transverseaxis, each of the one or more of laser diodes configured to emit a beamof light in an emission direction orthogonal to the transverse axis, theemitted beam diverging at a first divergence angle in a fast-axisdirection orthogonal to both the transverse axis and the emissiondirection, and diverging in a slow-axis direction at a second divergenceangle less than the first divergence angle, the slow-axis directionparallel to the transverse axis; a first cylindrical lens configured tocollimate and/or focus, in a fast-axis direction, the beam of lightemitted by each of the one or more laser diodes; a second cylindricallens configured to diverge, in a slow-axis direction, the beam of lightemitted by each of the one or more of laser diodes such that the beamsof light emitted by the one or more laser diodes overlap one another inthe slow-axis direction; and a scanner configured to controllably pivotthe linear beam of light about a pivot axis parallel to the slow axis.2. The system of claim 1, further comprising: a third cylindrical lensconfigured to, in conjunction with the first cylindrical lens, collimateand/or focus in a fast-axis direction the beam of light emitted by eachof the one or more laser diodes.
 3. The system of claim 1, wherein theemitted beams of light are collimated and/or focused in the fast-axisdirection such that a full-width half-magnitude (FWHM) portion of theemitted beams of light are less than or equal to a predetermined widthin the fast-axis direction at a predetermined distance from the system.4. The system of claim 3, wherein the predetermined distance is 150meters from the system and the predetermined width is 2 cm.
 5. Thesystem of claim 1, wherein the emitted beam of light has a wavelengthbandwidth of less than 3 nm.
 6. The system of claim 1, wherein theemitted beam of light has a nominal wavelength in the infrared band. 7.The system of claim 1, wherein the first cylindrical lens is a concavelens with concavity in the fast-axis direction.
 8. The system of claim1, wherein the first cylindrical lens is a convex lens with convexity inthe fast-axis direction.
 9. The system of claim 1, wherein the secondcylindrical lens is a concave lens with concavity in the slow-axisdirection.
 10. A method for projecting a linear beam of light on adistant object, the method comprising: emitting, by each of one or morelaser diodes distributed along a common transverse axis, a beam of lightin an emission direction; collimating and/or focusing, in a fast-axisdirection orthogonal to both the transverse axis and the emissiondirection, each of the plurality of beams of light so as to span a firstdivergence angle; diverging, in a slow-axis direction parallel to thetransverse axis, each of the plurality of beams of light so as to span asecond divergence angle less than the first divergence angle, whereineach of the diverged beams of light overlap one another in the slow-axisdirection; and controllably pivoting the linear beam of light about apivot axis parallel to the slow axis.
 11. The method of claim 10,wherein focusing, in a fast-axis direction, each of the emitted beams oflight results in a full-width half-magnitude (FWHM) portion of theemitted beams of light are less than or equal to a predetermined widthin the fast-axis direction at a predetermined distance from the system.12. The method of claim 11, wherein the predetermined distance is 150meters and the predetermined width is 2 cm.
 13. The method of claim 10,wherein controllably pivoting the linear beam of light about a pivotaxis comprising mechanically pivoting a projector about the pivot axis.14. The method of 10, wherein controllably pivoting the linear beam oflight about a pivot axis comprising energizing a particular laser diodebar of an array of laser diode bars.
 15. The method of claim 10, whereinthe emitted beam of light has a wavelength bandwidth of less than 3 nm.16. A system for projecting a linear beam of light on a distant object,the system comprising: an array of laser diode bars, wherein each of thearray of laser diode bars has a plurality of laser diodes distributedalong a common transverse axis, each of the one or more of laser diodesconfigured to emit a beam of light in an emission direction orthogonalto the transverse axis, the emitted beam diverging at a first divergenceangle in a fast-axis direction orthogonal to both the transverse axisand the emission direction, and diverging in a slow-axis direction at asecond divergence angle less than the first divergence angle, theslow-axis direction parallel to the transverse axis; a scannerconfigured to sequentially energize, one at a time, each of the array oflaser diode bars so as to scan the linear beam of light in a fast-axisdirection; a first cylindrical lens configured to collimate and/orfocus, in a fast-axis direction, the linear beam of light emitted by theenergized one of the array of laser diode bars; and a second cylindricallens configured to diverge, in a slow-axis direction, the beam of lightemitted by each of the one or more of laser diodes such that the beamsof light emitted by the energized one of the array of laser diode bars.